More than 95% of the leather manufactured in the U.S. is chrome tanned. Disposal of solid chrome wastes from the tanning process has become an increasingly serious problem to the leather industry. Chrome tanning generates approximately 54,000 metric tons of chrome waste annually in the U.S., about half in the form of chrome shavings. Sanitary landfills are reluctant to accept chromium-containing waste because of the potential for ground water contamination by toxic chromium compounds.
Chrome effluent from the bluing stage of leather tanning can usually be treated and then reused in the pickling or tanning process. Little, however, has been done with solid chrome shavings other than pressing them to form sheet-like products, or possibly hydrolyzing the shavings for chromium recovery.
Several Studies [Aunstrup et al., Brit. Pat. 1,243,784 (1968); Braeumer et al., Ger. Offen. 2,705,671 (1978); Leder- und Hautemarkt. Gerbereiwissenschaft und Praxis 30:100 (1978); Bronowski et al., Leder 30:8 (1979); Sauer et al., Leder- und Hautemarkt. Gerbereiwissenschaft und Praxis 36:70 (1984); Iliskovic et al., Koza Obuca 34(6):130 (1985)]have revealed that waste products from fleshing and beaming operations can be treated with enzymes at low temperatures for short periods of time to give products that have commercial value and/or are acceptable for disposal into municipal sewage systems. In contrast, previously disclosed procedures for treating solid chrome waste products usually are time-consuming or require boiling of the chrome wastes before enzymatic treatment [Suseela et al., Leder 34:82 (1983); 37:45 (1986); Parvathi et al., Leather Sci. 31:236 (1984); 33:8, 303 (1986); Monsheimer et al., Ger. Offen. 2,643,012 (1978); Hafner et al., Ger. (East) DD 212,983 (1984); DD 243,715 (1987)). Furthermore, in these processes, chromium is frequently dissolved and becomes difficult to separate from the hydrolyzed protein.
Heidemann [J. Am. Leather Chemists Assoc., 86:331-333 (1991)] proposes the use of proteolytic enzymes for better decomposition of chrome shavings after first boiling the shavings with calcium hydroxide. A minimum of about 1% enzyme is required and the protein hydrolysates are taught as being removed only after the enzymatic reaction.